Adjustable transmission line



ADJUSTABLE TRANSMISSION LINE Filed Feb. 27, 1945 3 Sheets-Sheet 1 METER osclLurron 53 DETECTOR INVENTOR.

NICHOLAS V. FEDOTOFF ATTORNEY p 1946- I N. V. FEDOTOFF 2,407,147

' ADJUSTABLE TRANSMISSION LINE Filed Feb. 27, 1945 3 Sheets-Sheet 2 s 8 FA g g x Q E INVENTOR.

NICHOLAS v FEDOTOFF g c9 E ATTORNEY N. V. FEDOTOFF ADJUSTABLE TRANSMISSION LINE Sept. 3, 1946.

3 Sheets-Sheet 3 Filed Fe b. 27, 1945 INVENTOR. NICHOLAS. V. FEDOTOFF AE'TORNEY Patented Sept. 3, 1946 2,407,147 ADJ USTAB LE 'TRANSMIS SION LINE Nicholas V. Fedotoff, Lynbrook, N. Y., assignor, by mesne assignments, to Hazeltine Research, Inc., Chicago, 111., a corporation of Illinois Application February 27, 1945, Serial No. 579,975

12 Claims. 1

This invention is directed to transmission lines ,of adjustable electrical length. While the invention is subject to a variety of applications, it is especially suited to short-circuited transmission linesand will be particularly described in that connection.

Short-circuited transmission lines of the type 'under consideration comprise a pair of conductors usually arranged in either spaced parallel or coaxial relationship to have uniformly distributed inductance and capacitance. The effective electrical length of such a line may be adjusted by means of a short-circuiting element bridged across and freely slidable along its conductors. Where the adjustmentof the short-circuiting element is such that the electrical length of the line plus its terminating impedance is equal to onequarter of its op'eratingwave length, or an in tegral multiple thereof, the line exhibits impedance characteristics analogous to those of contors and afiixed to, the tuning element, the link and tuning element together constituting atuning plunger axially movable along the line.

While arrangements of this type have proved to be operative, they have certain inherent limitations which may be objectionable in particular installations, For example, as the tuning plunger is withdrawn from the line to increase its electrical length, the over-all physical length of the arrangement is increased progressively. Where space limitations are important, this feature may be undesirable.

In another line structure of the prior art in which the conductors have a coaxial or concentric relationship, the inner conductor is rotatably supported and is provided with a screw thread adapted to engage a threaded bushing of the tuning element. Additionally, the tuning element is slidably mounted on one or more guide rods positioned in the interconductor space which lock the tuning element against rotation, With this ,con-

' ductor at ultra-high frequencies,

2 i struction, rotation of the inner conductor advances the tuning element along the line for tuning. This construction has the advantage that the physical dimensions of the structur do not vary with tuning. However, from a mechanical standpoint it is desirable that the inner conductor be made of steelbut steel is a poor con- Furthermore, it is necessary to lubricate the threaded portion of the inner conductor whereasbest operation of the line requires that its conductors be maintained clean. Additionally, the discontinuities in the skin of the inner conductor resulting from the screw thread may impair the conductive characteristics of the transmission line.

. It is an object of the invention, therefore, to provide a transmission line of adjustable electrical length which avoids one or more of the above-mentioned limitations of prior art arrangements.

It is a further object of the invention to provide an improved transmission line of adjustable electrical length having reduced space requirements.

, A, transmission line of adjustable electrical length in accordanceiwith the invention comprises a first conductor and a second Iconductor, the latter having an axially extending slot and a predetermined spaced relation to the first con- "ductor An adjustable member is movable in a predetermined path in the space between the conductors, for varying the electrical length of the transmission line including these conductors. The arrangement also comprises a driving member disposed within the second conductor for ex- ?Iting a controllable driving force along the line. The line also has means projecting through the slot of the second conductor into mechanicalcoupling engagement with theadjustable member and the driving member for effecting a displacement of the adjustable member along its path by the driving member,

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following descrip- I appended claims.

tion taken in connection with the accompanying drawings, and its scope will be pointed out in the tation of a wave meter arrangement utilizing the transmission line ofFigs. .1-3,inclusive; Fig. 5 is a cross-sectional view of a further embodiment of the invention; Figs. 6, 7 and 8 are additional sectional views taken as indicated by section lines 66, '|l and 8--8, respectively, of Fig. and Fig. 9 is a schematic circuit diagram of a poweri bridge network utilizing the transmission line of so as to have a predetermined spaced relation:

with reference thereto. A pair of centrally apertured end plates I2 and H) of conductive material are fitted to the opposite ends of conductor ID. A conductive bushing I4, inserted into the aperture of end plate l2 and nonrotatably supported thereby, is received by one end of conductor to establish the desired coaxial alignment of the inner and outer conductors. The alternate end of conductor II is supported in a manner described hereinafter, to complete the desired coaxial alignment of these conductors. One or more machine screws l5, locking conductor H to bushing I4, hold the inner conductor against rotation. An axially extendingor longitudinal slot I5 is milled into conductor I0 and similar but diametrically spaced slots l1 and- I8 are cut into conductor H. In assembling the line arrangement, its conductors areso oriented that slots I6, I! and I8 are in vertical alignment.

The transmission-line structure includes an adjustable membermovable in a predetermined path in the space between conductors I0 and II for varying the electrical length of the line constituted by, or including, these conductors. For the illustrated arrangement, this adjustable member short-circuits the inner and outer c'onductors to determine the electrical length of the line-and is provided by a ring 2!] having a series of resilient contact fingers 2| and 22 disposed about its inner and outer peripheries. Contact fingers 2| and 22 are suitably formed and proportioned to engage the inner and'outer conductors of the line so that the short-circuiting member is supported by and freely movable along these conductors in the space therebetween.

A driving member is disposed within the second or inner conductor ll of the line for exerting a controllable driving force therealong and for aiding in establishing the coaxial alignment of the inner and outer conductors. ber is provided by a rotatable shaft 24 a portion of which is threaded, as indicated at 25, to form a lead screw. One end of shaft 24 is rotatably supported in a bearing26 secured to a centrally located recess in the end of bushing l4 which is adjacent this end of shaft 24. Preferably, bushing 26 is constructed of an oil-impregnated material to be self-lubricating. The opposite end of the shaft is rotatably supported in a bearing 2'! retained in endplate l3 by means of retaining rings 23 and 29. This shaft also projects through a bushing construction 30 carried by the free end of conductor land serves to maintain the coaxial alignment of conductors I0 and H.

The'free end of shaft 24 extends beyond end plate I3 and supports a crank 3| through which the rotation of the lead screw may be controlled.

In order that the adjustable short-circuiting member 20, 2|, 22 may be selectively displaced along'the transmission lin under the. control of- This driving mem-- thereto.

lead screw 25, the line arrangement includes means projecting through the slots l1 and N3 of the inner conductor into mechanical-coupling engagement with both the adjustable short-circuiting member and the driving member 25. As illustrated in Fig. 2, this means consists of a threaded bushing 35 having diametrically opposed extensions 36 and 31. The threaded portion of the bushing engages lead screw 25 while the extensions 35 and 3'! thereof project, respectively, through slots l1 and I8 of the inner conductor tobe secured to the short-circuiting member by way of machine screws 38. Also, extension 36is sufiicientlylong to extend through longitudinal. slot |-B of outer conductor ID to serve as an indicator for permitting the position of the shortcircuiting member to be determined upon inspection. A calibrated scale (not shown) is associated with slot I8 so that extension 36, in conjunction therewith, provides a direct indication of the resonant wave length ofthe transmission line for each adjustment of its short-circuiting element.

An additional threaded bushing 40, having the same general configuration as bushing 35, is also included in the line arrangement. This additional bushing is slidable along a pair'of studs 4| and 42 extending from bushing 35. Each of the bushings is centrally recessed to house a helical spring 43. The added bushing, in conjunction with spring 43, constitutes an anti-backlash mechanism.

Energymay be supplied to or taken from the transmission line by means of pickup devices which may be accommodated by suitable receptacles 5E! and 5| projecting through conductor H! as clearly disclosed in Fig. 3. These receptacles are preferably diametrically opposed and therefore the circuit arrangements coupled thereto are shielded by the centrally located inner conductor The current-carrying elements of the line structure, suchas conductors l0 and H and contact fingers 2| and 22 may be formed of brass and are, preferably, silverplated to have improved conductivity characteristics. Shaft 24, however, is preferably machined from steel stock.

The illustrated embodiment of the invention effectively comprises a coaxial transmission line which is short-circuited at each end and may, therefore, be considered as a resonant cavity. The effective electrical length of the cavity is equal to one-half its resonant wave length and may be adjusted by displacing the short-circuiting member along its inner and outer conductors to tune the cavity over a predetermined range of operating wave lengths. In this connection it will be apparent that the wave-length range is determined by the permissible range of displacements of the short-circuiting member. Therefore, the physical lengths of conductors l0 and II, which are shown indefinitely in Fig. l, are selected with a view to obtaining a desired range of operating wave lengths.

The schematic circuit diagram of Fig. 4 represents the application of the described line arrangement to a wave meter system for determining the operating wave length of an oscillation generator 53. A coupling loop 52, coupled to generator 53 and extending into the resonant cavity by way of one of its receptacles or 5|, excites'the cavity. A second coupling loop 54 extending into the resonant cavity through the other of its receptacles couples a detector 55 The output circuit of the detector is coupled to a meter 55, such a'sa voltmeter- In operating the wave meter system, lead screw 25 is rotated by crank 3|. The slots of inner conductor II lock bushing 35 against rotation so that this bushing and the short-circuitingmember carried thereby are displaced along conductors I and II by lead screw' 25. This'adjustment of the short-circuiting member varies the electrical length of the resonant cavity, tuning the cavity over its range of operating wave lengths. When the effective electrical length of the cavity corresponds to one-half the operating Wave length'of the oscillator, a maximum deflection is obtained on meter 50. The operating wavelength of oscillator 53 may then be determined from the position of projection 36 with reference to the wave length scale associated with slot IS in conductor I0.

Figs. -8, inclusive, illustrate the application of the present invention to a transmission line including a pair of spaced parallel conductors associated with a bolometer element to be utilized as a component of a power-measuring bridge network. The line arrangement is enclosed within a conductive shield I00 having a circular cross section and conductive end plates I BI and I02.

The transmission line includes a first hollow conductor I03 having a longitudinal slot I04 and carrying at one end a conductive bushing I05 for effectively'extending the conductor. A second conductor has a similar construction and consists of a hollow conductivemember I06 with a longitudinal slot I01 and a conductive bushing I08. These conductors are assembled in spaced parallel-relationship, beingsecured atone end to suitable recesses in end plate I02 of the shield and being supported at their opposite ends by a disc I09 of insulating material and apertured to receive conductive bushings I05 and I08. Disc I09, in turn, is mounted by means of brackets H0 and III to a conductive collar II2 slidable along shield member I00. In order that collar as indicated at I I3 and I I4, the slotshaving suflicient widthto accommodate brackets H0 and I I I. A series of tabs I2I are struck out of collar IIZ, as shown in Fig. 8, and are depressed frictionally to engage shield I00.

A bolometer element II5, consisting of a center-tapped temperature-variable resistor enclosed within a glass envelope, is supported upon disc I09 by means of insulating, straps HE. A conductor I24 connects with the center tap of the bolometer and is drawn through an opening of shield I00 to connect the bolometer element into a bridge network. This element is also electrically coupled to conductors I03 and I08 by wayof connectors Ill and H8, extending from the opposite endsof the bolometer element to resilient contact fingers H9 and I20. Thesecontact fingers are secured to disc I09 and are suitably shaped to engage bushings I05 and I08 of the transmission-line conductors I03 and I05, respectively. The adjustable mounting of disc I09 is provided to permit adjustment of the coupling of the bolometer. element to the line conductors, for a purpose. to be made clear hereinafter; A pickup loop'l25 is received by apertures in comductive bushings I05 and I08 and serves to cou ple the transmission line to a circuit arrangement, such as an oscillation generator, for the purpose of making power measurements; This loop projects through an opening I26 of end-plate IOI and may be adjustedlongitudinally of the .line, by means of set screws. I21 andl28;

I I2 mayslide along the shield, the shield is slotted The effective electrical lengthof the transmission line, including conductors l03 and I06, may be adjusted by, means of a conductive short-circuiting member or yoke I which is supported by and freely movable along the line conductors. As illustrated in Fig. "7, the'short-circuiting yoke I30 is essentially a circular disc apertured to-accommodate conductors I03 and I06 and having resilient contact fingers I31 and I32 which engage the line conductor andafford a desired connection to the yoke. An indicator I33, secured to the upper section of yoke I30 and projecting through slot II 3 of the shield, enables the position of the short-circuiting member to be determined upon inspection. If desired, the shield may be suitably calibrated to indicate the operating wave length for particular settings of member I30.

As in the described Fig. 1 embodiment, the driving member for effecting displacements of, the short-circuiting yoke I30 along the line is provided by one or more lead screws rotatably disposed within the line conductors. Preferably, two

such lead screws are provided, onebeing indicated at I and disposed within conductor I03 while the other I is located within conductor I05. One end of each lead screw has a reduced cross section and projects through end plate I02 of the shield to support driving gears I42 and I43. A third gear I44, meshing with gears I42 and I43 and supported by a. stub shaft I45, provides a unicontrol for efiecting identical adjustments of lead screws I40 and MI. Stub shaft I45 is also rotatably supported within end plate I02 and carries upon itsfree end a crank I46 for controlling the driving members I40 and MI. I r

As illustrated in Fig. 7, yoke I30 is slotted to receive a pair of threaded'vanes I 50 and I5I which engage lead screws I40 and MI, respectively, for effecting displacements of the yoke member by the lead screws. Vanes I50 and I5I are locked in position by means of threaded pins I52 and I53 which project through aligned apertures in the yoke I30 and each of the vanes.

Fig. 9 represents a schematic circuit diagram of a bolometer-type power-measuring bridge network, utilizing the line arrangement of Figs. 5-8,

inclusive, for measuring the power output of an oscillation generator I55. The bridge network is similar to the well-known Wheatstone bridge in that it essentially comprises a network of resistors. Three of the arms or the bridge are provided by a variable resistor IBI for balancing the bridgenetwork in the face of ambient temperature variations, a variable resistor arrangement I62-calibrated with reference to bolometer element I I5 to read directly in terms of power and a'fixed resistor I03. The remaining arm of the bridge includes the line arrangement of conductors I03 and I00 and their associated bolometer element II5. The line arrangement; is:coupled into the bridge circuit by means of the conductor I24 extending from the mid-point of thebolometer element H5 and a second conductor I50 cou-- loop I25 inductively coupled thereto, as by? way of an inductor I55. While radio-frequency energy is applied to the bolometer element I I5 from transmission line conductors I03 and I00, only direct current is applied to'the bridge arrangement in view of the connection I24 to the midpoint. of the bolometer and conductor I60 to the shield.

In making power measurements, the bridge network is initially balanced by adjustment of resistor IGI but with the bridge decoupled from the oscillation generator. Having established the initial balance, pickup loop I25' is brought into inductive coupling relation with inductor I56 of the oscillation generator. The position of bolometer element II along transmission line I03, I06 as well as the position of its short-circuiting yoke I30 are then adjusted. to effect an impedance match between the line arrangement and the oscillation generator for maximum power transfer therebetween. By sliding the disc I09 to vary the position of the bolometer element with reference to the line conductors, an approximate or coarse impedance match is readily obtainable. Through crank I46 lead screws I40 and MI are rotated to displace the short-circuiting yoke I30 as required to perfect the impedance match.

It will be apparent from the adjustments described that the line arrangement is similar to an adjustable transmission line terminated in an impedance element and having a stub line for providing impedance-matching conditions between the terminating impedance and'a circuit to which the line is coupled. In other words, that portion of the line arrangement extending from the connections of the bolometer element H5 with conductors I03 and I06 and including pickup loop I25 may be considered as a line arrangement terminated in a resistive load. The remainder of the line arrangement between the connections to the bolometer element and the short-circuiting yoke I30 may be considered as a stub line, adjustable to efiect impedance matching between the composite line arrangement and oscillation generator I55. The energy transferred from the oscillation generator to the transmission line through the coupling between pickup loop I25 and inductor I50 causes a resistance variation in the temperature-variable condition in the bridge network and provide the desired indication of the power output of oscillation generator I55.

Each of the described embodiments of the invention features a line arrangement in which the space requirements are minimized. Thisresults from the fact that the physical dimensions of the line remain constant irrespective of the tuning adjustments. Also, in each cas the driving member for displacing the short-circuiting element is made of steel stock which is particularly desirable from the mechanical standpoint, while the line conductors have a construction desired to attain optimum electrical characteristics. Furthermore, the driving members may be lubrieated as required without disturbing the conductive characteristics of the line conductors.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A transmission line of adjustable electrical length comprising, a first conductor, a second conductor having an axially extending slot and a predetermined spaced relation to said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line includin said conductors, a driving member disposed within said second conductor for exerting a controllable driving force along said line, and means projecting through said slot into mechanical-coupling engagement with said adjustable member and said driving memberfor effecting" a displacement of said adjustable member along said path by said driving member.

2. A transmission line of adjustable electrical length comprising, a first conductor, a hollow second conductor having an axially extending slot and a predetermined spaced relation to'said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line including said conductors, a driving member disposed within said second conductor'for exerting a controllable driving force along said line, and means projecting through said slot into mechanical-coupling engagement with said adjustable member and said driving member for effecting a displacement of said adjustable member along said path by said driving member.

3. A transmission line of adjustable electrical length comprising, a first conductor, a second conductor having an axially extendin slot and disposed in spaced parallel relationship to said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line including said conductors, a drivingmember disposed within said second conductor for exerting a controllable driving force along said line, and means projecting through said slot into mechanical-coupling engagement with said adjustable member and said driving member for efiecting a displacement of said adjustable member along said path by said driving member.

4. A transmission line of adjustable electrical length comprising, a first hollow conductor, a second conductor having an axially extending slot and coaxially disposed within said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line including said conductors, a driving member disposed within said second conductor for exerting a controllable driving force along said line, and means projecting through said slot into mechanical-coupling engagement with said adjustable member and said driving member for effecting a displacement of said adjustable member along said path' by said drivin member.

5. A transmission line of adjustable electrical length comprising, a first conductor, a second conductor having an axially extending slot and a predetermined spaced relation to' said first conductor, an adjustable member supported by at least one of said conductors and movable therealong in the space between said conductors for varying the electrical length of the transmission line including said conductors, a driving member disposed within said'secondconductor for exerting a controllable driving force along said line, and means projecting through said slot into mechanical-coupling engagement with said adjustable member and said driving member for effecting a displacement of said adjustable member along said one. conductor by said driving member.

6. A transmission line of adjustable electrical length comprising, a first conductor, a second conductor having an axially extending slot and a predetermined spaced relation to said first conductor, an adjustable short-circuiting member engaging each of said conductors and movable therealong in the space between said conductors for varying the electrical length of the transmission line including said conductors, a driving member disposed within said second conductor for exerting a controllable driving force along said line, and means projecting through said slot into mechanical-coupling engagement with said adjustable member and said driving member for efiecting a displacement of said adjustable member along said conductors by said driving member.

7. A transmission line of adjustable electrical length comprising, a first conductor, a second conductor having an axially extending slot and a predetermined spaced relation to said first con ductor, an adjustable member movable in a pre-- determined path in the space between said conductors for varying the electrical length of the transmission line including said conductors, a driving member including a rotatable lead screw disposed within said second conductor for exerting a controllable driving force along said line, and means projecting through said slot into mechanical-coupling engagement with said adjustable member and said driving member for effecting a displacement of said adjustable member along said path by said driving member.

8. A transmission line of adjustable electrical length comprising, a first conductor, a second conductor having an axially extending slot and a predetermined spaced relation to said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line including said conductors, a driving member disposed within said second conductor for exerting a controllable driving force along said line, and means secured to said adjustable member and projecting through said slot into mechanical-coupling engagement with said driving member for effecting a displacement of said adjustable member along said path by said driving member.

9. A transmission line of adjustable electrical length comprising, a first conductor, a second conductor having an axially extending slot and a predetermined spaced relation to said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line including said conductors, a driving member including a rotatable lead screw disposed within said second conductor for exerting a controllable driving force along said line, and a threaded member extending from said adjustable member through said slot and meshing with said lead screw for effecting a displacement of said adjustable member along said path by said driving member.

10. A transmission line of adjustable electrical length comprising, a first hollow axially-slotted conductor, a second axially-slotted conductor 00- axially disposed within said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line including said conductors and having a projection extending through said slots of said first and second conductors to indicate the position of said adjustable member, and a driving member disposed within said second conductor for exerting a controllable driving force along said line and mechanically engaged by said projection for efiecting a displacement of said adjustable member along said path.

11. A transmission line of adjustable electrical length comprising, a, first axially-slotted conductor, a second axially-slotted conductor disposed in spaced relationship to said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varyin the electrical length of the transmission line including said conductors, a pair of similar driving members disposed within said first and second conductors respectively for individually exerting a controllable driving force along said line, unicontrol means for actuating said driving members, and means projecting through said slots into mechanical-coupling engagement with said adjustable member and said pair of driving members for effecting a displacement of said adjustable member along said path by said pair of driving members.

12. A transmission line of adjustable electrical length comprising, a first axially-slotted conductor, a second axially-slotted conductor disposed in spaced parallel relationship to said first conductor, an adjustable member movable in a predetermined path in the space between said conductors for varying the electrical length of the transmission line including said conductors and having a pair of projections extending through said slots of said first and second conductors respectively, a pair of similar driving members disposed within said first and second conductors respectively for individually exerting a controllable driving force along said line and mechanically engaged by said pair of projections for efiecting a displacement of said adjustable member along said path, and unicontrol means for actuating said driving members.

NICHOLAS V. FEDO'I'OFF. 

